The invention is in the field of optical networks. More in particular, it concerns an optical interconnection system for the realization of network elements in such networks, provided with one or more identical interconnection members.
Telecommunication techniques increasingly use optical signal transmission through optical fibre links. Various types of optical networks, not only single point-to-point connections, bit also tree-shaped, star-shaped, or ring-shaped interconnect structures using passive and/or active network components, have already been developed for this purpose, or are under development. Furthermore, optical networks are increasingly being expanded with protection configurations. Such diversity in network structures requires a large variety of network elements. Such network elements can vary from such relatively simple elements as optical amplifiers, filters, and transponders, and passive optical splitters, in some cases combined with optical amplifiers, to more complex elements such as optical add/drop multiplexers (AODMs) and optical cross-connects (OXCs). For reasons of economy, both manufacturers/suppliers and network operators of optical networks find themselves facing the technical problem of realizing the largest possible variety of network elements using the smallest possible number of equipment components, with which in addition, a high degree of flexibility regarding adaptation according to function and capacity of the network elements is to be achieved. In reference [1], and more in particular in Section 4 of said reference, a problem of this type is analyzed for Synchronous Digital Hierarchy (SDH) networks. The conclusion of said analysis is that the number of types of installation racks for the various equipment components can be minimized only if a rack structure is used with a uniform back panel; and that a uniform back panel can be used thanks to the application of a signal bus into which, inter alia, so-call aggregate and tributary interfaces can be plugged to realize signal connections in the various transmit and receive directions of the network elements in question. A rack structure with a back panel provided with a signal bus of this type not only allows for flexible adaptation to meet the current need for capacity of a network element, it also enables flexible upgrading to take place to more complicated network elements, e.g. from an ADM (add/drop multiplexer) to an LXC (local cross-connect). In principle, a signal bus rack structure of this type can also be realized in the optical domain. Reference [2] for instance, describes a possible development path to a xe2x80x98future nodexe2x80x99 based on an optical bus architecture, which may be ring-shaped. An optical bus of this type comprises a back panel with a number of parallel optical wave guides, on which, analogous to an electronic back panel, card-type modules fitted with optical circuits, hereinafter referred to as optical circuit modules, can be optically coupled. Typical problems that occur when optical power is drawn from optical conductors can be solved, e.g. by the application of optical fibre amplifiers in the back panel between the connection points. For the coupling of the optical circuit modules with each of the parallel wave guides in the Zoptical bus a technique is indicated which is known for example from reference [3]. In this reference, an optical bus is described consisting of a number of parallel optical fibres, D-shaped in section, in a back panel, to which card-type circuit modules are coupled with each of the optical fibres through specific connector blocks.
The application of a bus principle offers many advantages in the electrical domain. The application in the optical domain, however, is not as simple, since a signal bus is by principle a non-directional signal transport medium, whereas an optical wave guide, such as an optical fibre, is a directional signal transport medium. In addition, signal communication through a signal bus requires an additional bus protocol, calling for protocol conversions that can take place only in the electrical domain.
The purpose of the invention is to provide an optical interconnection system enabling a flexible realization of network elements. In doing so, it avoids the application of an optical signal bus, while still enabling a rack structure to be used with one or more identical interconnection members. It uses the insight that network elements in optical networks in most cases include a signal splitting function, and that a suitable manipulation of the optical signals is possible within the optical connections to and from the splitting means used, e.g. amplification, filtering, or regeneration.
An optical interconnection system for the realization of network elements in optical networks according to the introductory part of claim 1, and for the definition of which reference [3] has been used, according to the invention has the characteristic features according to claim 1.
Although in principle, optical fibre connections can be used bidirectionally, the risk of signal interference as a result of, inter alia, cross-talk will increase, and the bidirectional manipulation of optical signals is in most cases unfeasible, so signal traffic in either direction is preferably conducted through physically separate optical signal connections. In a preferred embodiment, the interconnection system according to the invention therefore has the characteristic features according to claim 2.
In order to offer an extra possibility for manipulation at the main ports of the optical signal splitters, a further preferred embodiment has the characteristic features according to claim 3.
The optical interconnection system according to the invention can also comprise more than one interconnection member. These members can be coupled together in various ways. According to a first variant of a coupling of this type, this can be implemented by connecting a pair of subsidiary ports of a member to the pair of main connection ports of a further member. For this purpose, a further preferred embodiment has the characteristic features according to claim 4. The coupling can also be effected by providing the member with a back panel onto which the row of module positions is fitted, in combination with a suitable positioning of the back panels of a number of interconnection members relative to each other in a rack or frame, and a design of the circuit modules that is adapted to this positioning. For this purpose, yet a further preferred embodiment has the characteristic features of claim 9.
Further preferred embodiments have been summarized in further subclaims.
Reference [4] discloses an optical interconnection apparatus for interconnecting via a back panel, using multiple fibre connectors, a number of printed circuit boards fitted with electrical wiring. These printed circuit boards are fitted with E/O and O/E converters that can be coupled to each other by means of multiple optical edge connectors connecting to optical fibre connectors located in grooves in the back panel, and also to external optical lines through separate optical connector points. However, there are no optical splitting devices in the back panel, and the purpose of the invention is not known from this.
Reference [5], which was not published in time, discloses an interconnection apparatus that provides optical and/or electrical signal interconnections of a number of input ports to a number of output ports through a segmentable signal bus. In this case an interconnection panel is used with a row of module positions for plugging in circuit modules, in combination with a set of circuit modules fitted with signal circuits with different bus functions. The signal bus can be composed of bus parts formed by permanent signal connections between subsequent modules and by the signal circuits of circuit modules plugged into the module positions.
The interconnection system according to the invention offers a relatively economical basic configuration for the implementation of a wide variety of network elements for various types of optical networks, which moreover can be expanded in a modular fashion without interruption of service, even to 100% of the optical fibre capacity of the connected optical fibre links.
[1] A. Herzberger et al., xe2x80x9cPHASExe2x80x94A comprehensive system for synchronous networksxe2x80x9d, Philips Telecommunication Review, Vol. 51, No. 2, pp. 4-17;
[2] I. M. Burnett and D. W. Smith, xe2x80x9cFuture switching requirements for telecommunication networks: Challenges for photonicsxe2x80x9d, ECOC ""93(?), TuP3.1, pp. 38-44;
[3] WO 95/20772;
[4] EP-A-0511779;
[5] Dutch patent application by applicant: application no. 1006239, application date Jun. 5, 1997.
All references are deemed to be incorporated in the present application.